Doctors have revealed a rising incidence of a flesh-eating disease which can kill up to half its victims. Young, healthy people with no external wounds have been found to be at risk from the bacteria, previously thought to attack elderly people, already weakened from other conditions, through an open cut. Twenty patients have been treated at the Queen Mary Hospital in Hong Kong in the past five years for necrotising fasciitis - a condition previously considered so rare that many doctors never saw it. Most sufferers were believed to have been infected by contaminated seawater, the hospital research has shown.